Total energy conservation system



J. L. BOYEN SERVATION SYSTEM March 12, 1968 TOTAL ENERGY CON 4Sheets-Sheet 1 Original Filed Dec. 18, 1964 INYENTOR. JOHN L. BOYEN Eownsmmflownsena JmDm n40 March 12, 1968 J. BOYEN TOTAL ENERGYCONSERVATION SYSTEM 4 SheetsSheet 2 Original Filed Dec. 18, 1964 tub;Oumu March 12, 1968 J. L. BOYEN TOTAL ENERGY CONSERVATION SYSTEM 4Sheets-Shee t 3 ori inal Filed Dec.

INVENTOR. JOHN L. BOYEN 'March 12, 1968 J. L. BOYEN 3,372,677

TOTAL ENERGY CONSERVATION SYSTEM Original Filed-Dec. 18, 1964 4Sheets-Sheet 4 /lO3o, IOSb, I03c Etc.

INVENTOR.

JOHN L. BOYEN BY 'loawsendW/ownsena United States Patent Ofilice3,372,677 TOTAL ENERGY CONSERVATION SYSTEM John L. Boyen, Orinda, Calih,assignor, by mesne assignments, to Vapor Corporation, Chicago, Ill., acorporation of Delaware Continuation of application Ser. No. 419,615,Dec. 18,

1964. This application Dec. 27, 1966, Ser. No. 604,945

5 Claims. (Cl. 122-7) ABSTRACT OF THE DISCLOSURE of the spiral to theouter end thereof and provisions for forcing the hot exhaust gases fromthe outer periphery of the spiral Water tube radially inwardly towardthe center of the spiral.

This is a continuation of United States patent application S.N. 419,615,filed Dec. 18, 1964, now abandoned.

This invention relates to an improved system and apparatus particularlyadapted to provide a high percentage of heat recovery from waste exhaustgases such as those from a gas turbine.

Recent improvements in gas turbines along with expanded demands forelectrical energy in many industries has resulted in an increase in theuse of such turbines for the generation of electrical energy at theimmediate site of use. This has occurred in small as well as medium andlarge industrial installations which also usually have a need for steamfor various production processes and/or plant heating or cooling.

The gas turbine exhaust is a source of heat which represents a plantenergy loss if not utilized. Such exhaust gases are usually in arelatively low temperature range, i.e., 750 to 1050 F., withoutsupplementary firing, but are suitable for steam generation by varioustechniques in the art of heat recovery boilers.

To obtain effective utilization of waste heat available from devicessuch as modern gas turbines, several problems must be reasonablyresolved simultaneously in a manner that has not been demonstratedentirely successfully in the prior art. Foremost among these is thedesign of a system whose interaction with the primary source of heataffords minimal interference with the latters operating cycle, e.g.reflecting a minimum back pressure to the primary exhaust source. Thesystem must also be able to produce maximum steam generation within aminimum time period in order to respond promptly to a variety of steamload needs within the main plant. Because waste heat recovery isgenerally an auxiliary type of equipment, i.e. secondary to the primaryelectrical energy generation of the turbine and generator combination,most modern industrial installations demand that the heat recovery unitbe limited to an absolute minimum in space. A typical installation, forexample, using a conventional heat recovery system capable of about 5000pounds of steam per hour, normally would entail an installation having aboiler section alone of about 20 feet in length, 8 feet of width andabout 10 to 12 feet of height with an additional clear space requirementfor tube removal of 16 feet. A comparable installation using the systemof this invention would only occupy a space of 7 feet by 9 feet by 6feet with a mini- 3,372,677 Patented Mar. 12, 1968 mum of additionalrequirement of clear space for tube removal.

Another problem encountered using conventional tech niques in thecontrol of gas flow into a heat recovery system is that at least twovalves are required to achieve proper hot gas inlet control, by-passcontrol and boiler isolation, when required. In using two valves ordampers to achieve these functions, it is very difficult to obtainproper balancing between the valve damper positions. This is made evenmore difficult when it is desired to tie in two or more hot gas exhaustsources to a single heat recovery unit with varying outputs from eachsource as is often the case in many industrial applications.

Thus it is an object of this invention to provide a heat recovery systemhaving a minimal effect on the primary power source by minimizingimposed back pressures while at the same time providing forautomatically balanced hot gas inlet, bypass and isolation. Forachieving this object the present invention includes a heat exchangerthrough which hot exhaust gases are directed, which heat exchanger isarranged to impose only slight resistance to gas flow, the amount ofresistance being substantially independent of the rate of gas flow. Thestructure atfording such mode of operation includes a heat exchangerthat has a gas path converging radially inwardly of a circle so that asthe gas velocity is reduced in response to cooling of the gas, thecross-sectional area of the gas flow path is correspondingly reduced.Automatic control of the system is thereby facilitated.

A feature and an advantage of this system is that the output of severalexhaust sources may be accommodated by a single unit with a little or noproblem in achieving proper balance between hot exhaust gas inlet andby-passQ Another object of this invention is to provide means in a heatrecovery system for automatic regulation of the hot waste gas sourceinlet and by-pass, the feedwater supply to the boiler, the water levelin the system, and the steam pressure at the output of the heat recoverysystem. In particular the automatic regulation of this inventionachieves equilibrium between the selective division of the flow of gasto the boiler and atmosphere, the flow of water provided by thefeedwater source, and a relatively constant predetermined level of steampressure at the outlet of the boiler and steam separator.

A further object of this invention is to provide a plenum or waste gasinlet chamber whose outlet may be auto matically and selectivelycontrolled to provide a regulated amount of hot gas to the boiler forcontrolled steam generation and expel any excess to the atmosphere. Afeature and an advantage of this arrangement is that more than one hotgas exhaust source may be handled without overheating the boiler tubebundle and while maintaining a controlled steam pressure at the output.

A further object of my invention is to provide a water tube boilerarrangement in combination with a steam separator which may accommodateforced feedwater recirculation to cause a surplus of water in the watertubes of the boiler. In this manner optimum heat transfer boundaryconditions are maintained between the internal fluid of the steamgenerating boiler, the water tubes themselves, and the heat transferredfrom the counter flow hot gas source exterior to the tubes. A featureand and advantage of this arrangement is that maximum steam generationmay be accomplished within a very few minutes of the time the hot gasesare introduced to the heat recovery system.

Another object of my invention is to provide automatic safety featureswhich prevent the system from devel0ping hot spots" on the boiler coilsand, in the event that the feedwater source or pressure the atmosphere.

I should fall below a cer-: tain predetermined value, shun-t allincoming hot gases to It is a further object to provide a combination ofantomatic controls whereby a given predetermined steam pressure andvolume output may be obtained from the system without reliance uponhuman operational skills and to provide for shut down of the system whensuch output tends to become excessive.

It is also an object of this invention to provide the system with anovel form of water tube boiler which utilizes a special spiral pancakearrangement of finned water tubes to 'achieve a minimum pressure drop ofthe hot gases passed therebetween while producing turbulence in the gasflow. The tube arrangement is such as to achieve counterfiow between thewater being heated internally and the hot gases passing the tubesexternally.

A feature and advantage of the spiral tube arrangement of my inventionis that a minimum of space is required for tube removal and maintenanceand that a large part of the maintenance of such a boiler may beeifcctuated with the tubes in place.

Another advantage of the finned tube spiral arrangement is that thisnovel design achieves maximum turbulence of the heating gases and hencemaximum heat transfer efiiciency and a minimum period to achieve steamoutput generation.

Another object of this invention is to provide a single gas valve tocontrol both hot exhaust gas admission and by-pass with a single gasdamper. A feature and advantage of this arrangement is that one valveperforms three functions; namely, inlet control, by-pass control, andboiler isolation when in a closed position. Normally these functionswould require at least two valves using conventional techniques.

Another feature and an advantage of the design of my invention is thatit makes possible standardization of design and to satisfy virtually allapplications with a single casing construction and a standard heatingsurface element. The inlet for the exhaust heat gas may be located inany of a number of different locations and may take the form of either asingle inlet in the front or an inlet at the side or an inlet at thebottom to accommodate different turbine arrangements and numbers ofturbines. A removal cover at the top of the boiler enclosure makes theentire water tube assembly accessible for cleaning or complete removal.The insulated casing assists in sound attenuation and if additionalsound attenuating material in the by-pass and inlet ducting is required,this may all be confined to the gas control rather than the whole boilersystem including by-pass ducting as is required using known techniques.

Numerous other objects, features and advantages of my invention willbecome apparent from a reading of the detailed specification thatfollows which shows one embodiment of my invention which I have foundsatisfactory under actual operating conditions.

Turning now to the drawings,

FIG. 1 is a schematic flow diagram showing my entire total energyconservation system;

FIG. 2 is an electrical schematic diagram and a portion of the pneumaticnet-work associated with the system shown in FIG. 1;

FIG. 3 is a partial cross-sectional elevation of a portion of the systemshown in FIG. 1; and

FIG. 4 is a plan view taken along line 4-4 of FIG. 3.

This invention embodies apparatus which provides a high percentage ofheat recovery from turbine exhaust gases by conveying the latterdirectly through a plenum and by-pass chamber to a compact water tubebundle wherein usable steam is generated. Forced recirculation isutilized to provide at least 50 percent excess water in the tube bundle,and the steam generated therein is subsequently separated by apparatusexternal to the tube bundle. The exhaust gases pass through a variableby-pass valve arrangement so that steam generation within the water tubebundle may be varied by the setting of the by-pass valve as the steamdemand requires. The entire unit may be matched to the characteristicsof the individual gas turbine to which it is connected including theminimization of back pressure. Because forced recirculation of waterthrough the tube bundle is provided, full steam production generally maybe attained in a very few minutes under normal load conditions. Gas fiowis normal to the tube surfaces and is caused to be highly turbulent.This feature combined with the forced water recirculation in the watertubes achieves a heat transfer capability many times higher per linealfoot of tubing than other types of heat recovery boilers which I amfamilar with. Such increase in overall system efiiciency allows asubstantial reduction in space required per lb-hour of steam outputcompared to other types of heat recovery systems which might be adaptedto gas turbines. The space requirement reduction also yields substantialsavings in site construction, installation, and transportation costs.

The invention is best understood by referring first to FIG. 1 which is aschematic flow diagram of my overall total energy conservation system.At the left side of the figure there is shown generally a gas turbinepower unit comprising compressor 1, combustor 2, and gas turbine 3assembled together in a conventional manner. Under normal runningconditions, the turbine unit takes in air at the left side of thecompressor as shown, while gas fuel is introduced to the combustor forignition with the compressed air delivered from the compressor; the highenergy jet of ignited fuel is then caused to impinge during itsexpansion upon the blades (not shown) of gas turbine 3 and causerotation thereof. The rotational energy thus generated is used to turnthe compressor and, through appropriate couplings and gearing, may beused also to turn dynamo or alternator 4- for the generation of DC. orAC. electrical energy. The output of the electrical generator then maybe distributed to various points of electrical power consumption; forexample, in a process plant, office building, hospital or the like.

The hot exhaust gases indicated by arrows 11 expelled by the gas turbineare conveyed by means of duct. 12 to gas plenum and by-pass valvehousing indicated generally at 13. The hot gases are then diverted inwhole or in part, further explained hereinafter, into the tube bundlecasing indicated generally at 14 wherein the hot gases come into contactwith the steam generating Water tubes having water recirculatedtherethrough in at least 50% excess over the amount of steam generated.After heating the water tubes, cooled exhaust gases 11a are combinedwith any hot exhaust gases 11b which may have been bypassed away fromthe water tube bundle by the by-pass valve. The combined exhaust gasesare then expelled through stack outlet 13a.

The fluid output of the water tube bundle, which is a mixture of steamand excess water, may be nozzled via conduit 15 into a cyclone steamwater separator of a type similar to that shown in my copending patentapplication, Method and Apparatus for the Cyclone Separation of Steamand \Vater Mixtures and the Like, Ser. No. 339,512, filed in the US.Patent Oflice on January 22, 1964; however, other conventional means ofsteam separation known in the art may be utilized. I prefer my ownseparator because I believe it yields the highest quality of steamavailable from a given mixture with a minimum of separator equipment andspace. The high quality steam emanating from the separator conveyedthrough conduit 16 which is also in fluid communication with the steamsafety pressure switch 17, safety valve 18 and conduit 19 which is influid communication with steam pressure proportional controller 28-, aconventional device which is indicated also in FIG. 2.

The water flow arrangement for my total energy conservation system isshown in the lower right hand portion of FIG. 1 and, as mentioned above,is of the type that maintains forced circulation of the water throughthe steam generating water tube bundle of the unit. This is accomplishedby means of pump 21 which draws water from reservoir 22 through piping23 past flushing connection plug 24, normally open isolating globe valve26, ad jacent normally closed blow down valve 27, and a conventionalstrainer assembly indicated generally at 28. The outlet of recirculatingpump 21 is connected to piping 29 and hence to the water tube bundle ofthe boiler housed in casing 14. Normally open separating globe valve 31and normally closed flushing connection valve 32 are provided in line 29for maintenance and cleaning. Differential pressure switch 33 isconnected across pump 21 and linked electrically to the bypass valve airmotor controller indicated generally at 34.

Recirculating pump 21 is driven by motor 35, also shown in FIG. 2,energized either by manual means or automatically upon commencement ofoperation of the turbine power unit. The sequence of these operationsand certain electrical safety features are explained in greater detailbelow.

Reservoir 22 is in direct gravity fluid communication with the steamwater separator to collect and provide preheated water for the forcedrecirculation through the boiler tube bundle. To make up for waterlosses and that converted to steam, a fecdwater supply is provided. Feetwater from outside source pipe line 41 is constantly supplied byfeedwater pump 42 through line 43 which communicates through feedwatermodulating valve 44, also shown in FIG. 2 and explained below. Feedwaterbypass valve 45 is normally closed and feedwater by-pass valve 46 isnormally open. After passage through the feedwater modulating valve, thefeedwater passes through normally open feedwater by-pass valve 47,through inlet check valve 48, inlet stop valve 49 and hence through theremainder of conduit 43 to reservoir 22.

Feedwater modulating valve 44 is controlled by con-- ventional feedwaterlevel controller 51, which is in fluid communication with reservoir 22through conduit 53 and the lower portion of the separator shell throughconduit 54. As the reservoir water level raises or lowers variableresistance arm 51a, shown in FIG. 2, the feedwater level controller isvaried to change the setting of the feedwater modulating valve 44. Bysuch variable modulation of valve 44 to control the flow of feedwater asa function of the water level in reservoir 22, the reservoir water levelis maintained between certain preselected and desired limits.

As one of several safety features to be explained in relation to myinvention, high water sensitive cut-off switch 58 and low watersensitive cut-off switch 59, also shown in FIG. 2 with their electricalfeatures as a part of the r electrical control circuitry, are connectedto each side of the feedwater level control by means of conduits 56 and57. The elevation of switches 58 and 59 are at the safe upper and lowerlimits, respectively, of the water in the separator and reservoir. Whenthe water level in the reservoir and steam water separator combinationexceeds a certain preselected level, indicated by the position of thehigh water cut-off switch, said switch responds to close a contact in anelectrical circuit, explained more fully hereinafter, which causes a redwarning light to be energized. At the same time the feedwater levelcontroller also responds to completely turn off feedwater valve 4 thuspreventing additional feedwater from being introduced into the systemuntil steam generation has caused the excess water level to drop.

Low water cut-off switch 59, similar to the high water cut-off switch,is adapted to close its contacts when the water level in the reservoirreaches a certain preselected low level indicated by the position ofswitch 59. When this low level of water occurs in reservoir 22, closingswitch 59 contacts, a red warning light is illuminated and the by-passvalve air motor solenoid controller 34 is cleenergized. This causesturbine exhaust gas damper 82, shown in FIG. 3, to move to the positionindicated by dashed lines at 82a which causes all hot turbine exhaustgases introduced to the gas plenum and by-pass valve chamber to beexpelled to the atmosphere through stack gas outlet 13a.

In addition to the safety features noted above, water pressure sensitiveswitch 60, shown in FIG. 1, is connected directly upstreamand downstreamof the feedwater supply pump 42; if the feedwater supply pressure shoulddrop below a certain preselected level, switch 60, which is alsoelectrically connected to the by-pass valve air motor solenoidcontroller, closes its contacts to cause complete by-passing of the hotturbine exhaust gases away from the water tube bundle and henceimmediate attenuation of the steam generating process. Such bypasscontinues until feedwater pressure is again present at the outlet of thefeedwater supply pump at which time pressure switch till is caused toopen its contacts, restore damper 82 to a normal operating position, andcause steam generation to resume.

Reference is now made to FIG. 2 of the accompanying drawings showing theelectrical schematic diagram associated with my total energyconservation system and basic ilow arrangement described above.

My invention is capable of either automatic or manual electrical controlas indicated by the four sections of selector switch SS designated SS1,2, 3 and 4. As shown in FIG. 2, the selector switch is in the automaticposition causing power on lamp 71 connected across the v. A.C. pilotcircuit legs P1 and P2 to be illuminated. All pressure and levelsensitive electrical switches are shown in normal operating positionwith hot exhaust being delivered from the gas turbine. When the turbinepower unit shown in FIG. 1 commences operation, a relay, K9, not shownin the accompanying drawings, is energized whereby contactors K9D andK9B are closed.

With the closing of K9D, relay SR is energized thus closing normallyopen contacts SR1, SR2, and SR3 which causes power from externalelectrical power source legs L1, L2, L3 to energize recirculating pumpmotor 35. Pump motor 35 in turn rotates recirculating pump 21, as shownin FIG. 1, to cause forced recirculation of water through the water tubebundle indicated at 101 in FIG. 3, and housed within housing 14 shown inFIGS. 1 and 3. At the same time normally closed contactor SR5 is openedto cause recirculating pump red warning lamp 72, which is in series withcontactor SR5 and together with its connected across lines P1 and P2, tobe deenergized. At the same time, recirculating pump on light 73connected across relay SR is energized.

With the closing of contactor K9B noted above, current is conductedthrough normally closed contactors CR1, 2, 3 and 4 to energize bypassvalve air motor controller solenoid valve 61. With solenoid valve 61energized, by-pass valve air motor 68 operates to position hot exhaustgas lay-pass valve 82 shown in FIG. 3. The position that the :air motorcauses by-pass valve vane 82 to hold is regulated by the output steampressure measured in conduit 19 by means of conventional proportioningcontroller 20. By this regulation, the amount of hot gas delivered tothe water tube bundle is controlled; and hence the output steam inconduit 19 is regulated and maintained at a preselected steam pressure.

As shown in FIG. 2, under normal operation, solenoid valve 61 isenergized and its three-way valve port 61a displaced in the direction ofarrow 63 to cause fluid communication of air from the controlled airoutput of controller 20 through the normally closed (shown in the openoperation condition) and common connection ports to air line 64b.Proportioned steam pressure controller 20 is connected at its steaminlet port to main header 19 and at its air inlet port to conduit 65a,which is a branch of air supply 65, through a conventional air filterand regulator indicated generally at 66a. The other half of the dividedair supply communicates through the filter and regulator indicatedgenerally at 66b and thence through conduit 65b to air motor 68. The airmotor is pneumatically coupled to air cyclinder 69 and both aremechanically linked to arm 81 which is directly coupled by shaft 81a toby-pass valve vane 82, FIG. 3, within the chamber indicated generally at13 and shown in FIGS. land 3.

Air motor 58 is controlled in the amount of its displacement, i.e., thedegree to which it opens or closes by-pass vane 82 by the movement ofarm 81, by means of a conventional positioner 68:: which in turn iscontrolled by the pressure of the air caused to pass through conduit64b. The greater the pressure of air passed through line 64b, thefurther positioner 68a causes air motor 68 and cylinder 69 to rotate arm81 and vane 82 in the direction of arrow 83a; the greater the amount ofhot exhaust that is caused to contact the boiler water tubes; and thegreater the amount of steam generated. Conversely, if the air pressuredrops in conduit 64b, positioner 68a causes air motor 68 to lower itsoutput; and conventional spring returns (not shown) in both the motorand cylinder 69 causes arm 81 and vane 82 to rotate in the direction ofarrow 83b thus causing by-pass of the hot gases away from the boilerwater tubes. Complete loss of air to positioner 68a causes completebypassing of the hot gases and stopping of steam generation. If anelectrical failure should occur, or if any of contacts CR1, 2, 3 or 4open, solenoid valve 61 is deenergized, three-way portion 61a rotates ina direction opposite the arrow 63, and positioner 68a is vented to theatmosphere causing air motor 68 to minimum displacement. This causesvane 82 to a position which bypasses all hot exhaust gases from the gasturbine to the atmosphere.

Proportional controller 20 is one that I have found satisfactory in myinvention, although other pneumatic designs might function equally wellin its place. This particular controller is provided with an adjustableset point and proportional band so that it may be set to deliver a givenair pressure signal to the air motor positioner with a predeterminedsteam pressure at conduit 19 and hence cause the gas by-pass vane tomaintain a position that causes delivery of the predetermined steampressure. If the steam pressure falls or rises, the proportionalcontroller delivers more or less air pressure, respectively, to the airmotor positioner and the steam generating process is altered tocompensate accordingly. Although it is possible to utilize other typesof proportional controllers, e.g., types using electrical or pneumaticpositioner controllers with an electrical by-pass valve modulatingmotor, I prefer pneumatic control since its characteristics tend toeliminate hunting of the by-pass valve.

In the event that the water level in reservoir 22 shown in FIGS. 1 and 3drops to a predetermined dangerously low level, low water switch 59,shown in the schematic diagram of FIG. 2 and in FIG. 3, is closedenergizing relay RI and low water level warning light 74 connected inparallel with said relay. In addition, if desired, alarm bell 75 shownin dotted line connected to terminals AT and AT2, is caused to besounded. Simultaneously, normally closed contactor CR1, shown in circuitleg SV, which energizes controller solenoid valve 61, is opened andcauses the solenoid valve to be tie-energized. As explained above, thiscauses exhaust gas by-pass valve vane 8-2 to move in the direction ofarrow 83b shown in FIG. 3, to by-pass all hot exhaust gases throughstack gas outlet 13a. When the water level in the reservoir returns toits minimum normal position, water level sensitive switch 59 opens andrelay R1 is de-energized; the red indicator light de-energizes; thealarm bell, if used silences; normally closed contactor CR1 againcloses; and operation of the entire system resumes with a selectedamount of gas turbine exhaust gas being conveyed to the water tubebundle.

In the event that the water level in reservoir 22 shown in FIGS. 1 and 3rises to a predetermined and undesirably high level, high water switch55, shown in the schematic diagram of FIG. 2, is closed energizing lowwater level warning light 76. In the particular embodiment of myinvention as shown in the accompanying drawings, I do not include arelay in series with the high water level switch similar to that shownand described above in respect to low water switch 59. Although such arelay could be added for operation with a contactor such as contactorCR4 shown in circuit leg SV similar to that described above for lowwater switch 58, this is not as necessary a safety feature for highwater cut-off as it is for low water. This is so because, unlike toomuch water in the system, excessively low water may result in permanentdamage to the water tubes and other vital components in a relativelyshort period of time if the hot gases are not by-passed; and relianceupon an operators response to visual and even audible alarms carries tooheavy a burden of risk. On the other hand, excessive water in the systemwill not cause immediate damage, and the action of the feedwatermodulator causes discontinuance of water flow to the boiler. In themeantime, hot gases which are caused to continue flowing into the plenumwill tend to deplete the excess water by steam generation and return thesystem to normal operation without interruption of steam generation.Reliance upon the operators observance of the warning light to checksuch return to normal does not present excessive risk to the system.

In the event that steam pressure present at the steam pressure safetyswitch 17, shown in F168. 1 and 2, exceeds a certain predetermined safelevel, the corresponding contacts shown in FIG. 2 are closed therebyenergizing relay R2 and warning red light 77 in parallel therewith. Inaddition, if an alarm bell is provided, as shown by the phantom linesindicating its connection between terminals ATS and AT4, such alarm willbe caused to sound. Simultaneously normally closed contactor CR2 isopened and controller solenoid valve 61 will be deenergized to cause thehot exhaust gases to be expelled through stack gas outlet 13a. Thisimmediately attenuates further steam generation in the water tubebundle. Upon return to the preselected normal minimum safe level forsteam pressure as sensed by pressure switch 17, relay R2 is deenergized;red warning lamp 77 is deenergized; the alarm hell, if any, connectedbetween terminais AT3 and AT4 is silenced; normally closed contactor CR2closes thus energizing controller solenoid valve 61; and hot exhaustgases may again be conveyed to contact the water tube bundle generatingsteam within the unit.

In the event that the diiferential pressure across recirculating pump 21shown in FIG. 1 should fall to a preselected low, indicating that theflow of recirculating water has been reduced below the level of safewater replenishment, the contact shown at differential pressure switch33 in FIG. 2 is closed thus energizing relay R3; red warning lamp 7'8 inparallel therewith; and, optionally, the alarm bell shown in phantomline connected between terminals ATS and AT6. Simultaneously, normallyclosed contactor CR3 is opened and the hot gas turbine exhaust gases arecompletely shunted away from the Water tube bundle and out through gasstack 13a. Upon return of proper differential pressure acrossrecirculating pump 21, differential pressure sensitive switch 33 isopened; relay R3 de-energized; alarm lamp 78 de-energized; the alarmbell, if used, between terminals AT 5 and AT6 is silenced; and contactorCR3 is returned to its normally closed position to cause the controllersolenoid valve to be re-energized and hot gases again directed inpreselected amounts upon the water tube bundle.

Should the recirculating pump motor 35 cease operating due to thermaloverload, thermal overload elements 35a and 35b provided as shown inFIG. 2 in power legs L1 and L3 open and disconnect the motor from theline. With this condition, pump 21 stops rotating and steam generationis turned off by the action of differential pressure switch 33 asexplained above. Additional overload protection for the recirculatingpump motor is provided by an overload relay, not shown, but whosenormally closed contacts 350 and 35d are shown connected in series withrelay SR. When current is interrupted to relay SR by the opening ofeither overload contactor 35c and 35d, normally closed contact SR5,normally held open by the current through relay SR, is caused to closeso that red warning lamp 72 is energized.

Connected across 115 volt A.C., 6O cycle, pilot circuit line legs P1 andP2 is 115 volt A.C., step-down, transformer 62 whose 24 volt A.C. outputenergizes modulating feedwater valve 44. The modulation of valve 44 isaccomplished by conventional techniques known in the electrical art andthe level of the water in reservoir 22 raising and lowering resistor arm51a. In the event of a rising water condition in reservoir 22, whichcould eventually also cause high water switch 58 to close and initiate asequence of steps described hereinabove, resistor arm 51a is elevated tocause the modulating feedwater valve to be driven toward the OEposition. This diminution of water flow through valve 44 persists untiladditional steam generation within the water tube bundle depletes theexcess water supply in reservoir 22. This in turn causes resistor arm51a to lower and drive the modulating feedwater valve toward the openposition to cause teedwater to pass again into the reservoir. In actualoperation, after the start up period, an equilibrium point is reachedwherein steam generation and feedwater recirculation become stabilizedin a steady state condition subject to change in the event of a changein steam demand, reaction by any one of the above described safetyfeatures, or shut down of the system. Shut down of the system may beaccomplished either automatically by de-energizing relay K9 (not shown),which causes contactors K913 and D to open, or by moving the selectorswitch from the automatic position shown in FIG. 2 to the oil positionindicated therein.

Although the foregoing specification describes one embodiment of myinvention with the selector switch having sections generally indicatedat SS1, SS2, SS3 and S54, all shown in FIG. 2, in the automaticposition, the system may also be operated manually. This is accomplishedby moving the ganged selector switches to the position marked man, ormanual, whereby the leads of power circuit legs L1 and L2 are moved fromtheir respective automatic positions shown in FIG. 2 to the indicatedman. or manual positions. When the switch to manual position is made,contactor K9D is disconnected from the circuit and contactor K9B isby-passed as indicated in the schematic diagram. When contactor K91) iseliminated from the circuit, the recirculating pump motor is energizedby depressing pump start button 91 which then completes the pilotcircuit power through relay SR and events commence as describedhereinabove for automatic operation. In addition, when the selectorswitches are set for manual operation, nonmally open contactor SR4,connected electrically in parallel with pump start but ton 91, is closedby the energization of relay SR. This is a conventional seal-in circuitarrangement whereby when the pumps start button is released, and thespring return opens the button circuit itself, current is still suppliedto relay SR through contactor SR4 and the pump stop button, which isnormally closed, to complete the circuit through contactors 35c and 35:1to pilot circuit leg P2.

All safety features and operation of relays R1, 2 and 3 may occur in themanual condition in a manner similar to that as described above in thecase of the automatic condition.

The system may be shut down manually by depressing off button 92. Thisopens the circuit to relay SR which causes pump motor 35 to shut-off andconsequently discontinue pilot circuit power to solenoid valve 61 andtransformer 62. This causes both the feedwater supply and the hotturbine gases to the boiler tubes to be shut off.

Having explained my invention in respect to steam flow generally, waterrecirculation, and the interaction of various pneumatic and electricaldevices therewith, attention is now directed to FIG. 3 which shows ingreater detail the hot gas by-pass chamber, Water tube boiler, and steamseparator.

Hot gases exhausted from the turbine shown in FIG. 1 are conveyed in thedirection of arrows 11 to the hot gas plenum indicated generally at 13via inlet conduit 12. Depending upon the setting of by-pass valve damper82, a function of the operation of various components of my invention asexplained hereinabove, a portion of the hot exhaust gases indicated byarrows 11b are by-passed directly through outlet stack 13a. Theremainder of the hot gases are deflected in the direction of arrows 11aand are directed inwardly to the tube bundle enclosure indicatedgenerally at 14. This chamber primarily houses two major components ofmy invention; the tube bundles indicated generally at 101 and thecentrifugal steam water separator indicated generally at 102. Althoughvarious types of steannwater separators may be used in my invention, Iprefer the use of my centrifugal steamwater separator as shown in myco-pending application and referred to earlier herein.

The water tube bundles generally indicated at 101 comprise a stack ofspiral tubes indicated generally at 1533a, b, 0, etc., and shown ingreater detail in FIG. 4. Each coil comprises a flat, spirally coiled,tube element. These are arranged, or stacked, vertically and attached toa vertical inlet header 104 which is in fluid communication withrecirculating pump outlet piping 29 shown in FIG. 1. Vertical outletheader 106 is in fluid communication with each spiral coiled tubeelement at the outermost terminus of each spiral by means of the severaltubes 109. With this arrangement each tube element represents a parallelflow path for the water and steam generated mixture circulating frominlet header 104 toward oulet header 106 and hence to the separatorindicated generally at 102. The gas flow indicated by arrows 11a in FIG.3 is radially from the outside of the tube assembly to the interiorthereof. As the hot gases flow through the tube assembly, they arecooled and their velocity tends to drop. However, simultaneously, thecross sectional area of the assembly is decreasing so that the gasvelocity actually remains almost constant. This results in almostoptimum heat transfer conditions in all parts of the tube assembly.Since the water flow is from inside header 104 to outside header 106,desirable counterflow conditions between the hot gases on the outsideand the water being heated inside the tubes prevails. After the gaseshave passed the tubing in counterflow passage, and heat transfer hasoccurred to produce the steam water mixture in header 106, the gasesflow through and join the earlier by-passecl gases indicated by arrows11b for egress through stack 13a. In this invention the hot gases arecaused to flow through a relatively unrestricted path to heat the watertubes. This design in combination with the novel configuration of thewater tube pancake stack causes a minimum pressure drop to developbetween inlet conduit 12- and outlet exhaust stack 13a and, in turn,causes minimum back pressure to be imposed on the gas turbine generallyindicated at A in FIG. 1.

Each fiat spirally coiled tube element indicated generally at 103a, b,etc., in FIG. 3, and best shown singly in FIG. 4, comprises curved inlettube 107, finned spiral portion 108 and curved tube outlet portion 109.In a typical arrangement of the spiral tube element, two normal spiralturns as indicated by center lines 111 and 112 are followed by a widerspacing 116 before repeating normally spaced center lines 113 and 114.Interval 116 between center lines 112 and 113 is greater than theinterval 117 between center lines 111 and 112 or interval 118 betweencenter lines 113 and 114. As a result of this configuration, spaces areprovided such as those indicated by dimensions 115 and 121 between theoutermost finned surfaces of every two turns of the spiral coil tubeelement. The existence of such gaps, and space 123 between the innermostspiral and inlet header 194, further minimize the pressure drop throughthe tube system by forming unrestricted spaces for gas flow. These samespaces provide ready access between the tubes to permit cleaning agentsand tools to be manipulated therebetween and clearance to facilitateproper maintenance.

Tubing 108 is of the finned type and although a variety a such tubing isreadily available, I have found extended surface tubing having a 1.25inch 0.1). and a .095 inch wall to be satisfactory. Heavier walledtubing may be employed if required by pressure conditions. T he .095inch wall tubing which I employ is provided with fins 1124, ten fins perlineal inch, and may be ASME specification SA 178 or equal. The heatingsurface of the tubes is thus 2.3 square feet per lineal foot. Radialfins 124 are segmented to produce maximum turbulence of the passinggases and circumferentially welded to insure optimum heat transfer.These fins increase the heat transfer capability per lineal foot oftubing to approximately eight times that of plain tubing.

The use of extended surface or finned tubing with a relatively largeinside diameter to form the spiral tube elements minimizes the effect ofthroughput caused by scale forming materials which may be in thefeedwater. The relatively heavy walled tubing used minimizes the harmfuleffects of pinpoint or pitting type corrosion and greatly extends thelife of the boiler. All pressure welds, such as those connecting curvedtube portions Hi7 and 189 to headers 1434 and 106, respectively,preferably are both tested hydrostatically at not less than 1 /2 timesdesign pressure and inspected in accordance with the ASME code.

Although I have described my invention in some detail in the foregoingspecification, this has been done by Way of example for purposes ofclarity of understanding and is not intended to impose unnecessarylimitations upon my invention. It is understood that my invention may beprac ticed in a great variety of versions substituting, changing, ormodifying various components while using the system which I havedisclosed and remaining within its spirit and the scope of the appendedclaims.

What is claimed is:

1. Apparatus for exchanging heat between a first fluid and a secondfluid having a ditferent temperature from the first fluid comprising atleast a pair of stacked hollow fluid impervious tubes that areparallelly spaced apart to define a radial fluid path therebetween, eachtube being formed into a convoluted spiral of substantially planarconfiguration and having an inlet at the inner spiral extrcmity thereofand an outlet at the outer spiral extremity, means for conveying thefirst fluid to said inlet ends and exhausting the first fluid from saidoutlet ends so that in traversing each said tube the first fluidadvances radially outwardly of said spiral, and means for forcing thesecond fluid along said radial fluid path from the periphery of thespiral tube configuration radially inwardly to the center thereof in thespace between said pair of tubes and counter to the first fluid in saidtubes.

2. I11 a waste heat recovery system having a hot gas source, thecombination comprising: an insulated enclosure having a hot gas inletand an exhaust outlet; a plenum having an inlet in fluid communicationwith said hot gas source and an outlet in fluid communication with saidgas inlet; damper means mounted in said plenum to regulate the amount ofgas communicated to said enclosure; water tube boiler means having aninput header and an output header mounted within said enclosure toproduce a mixture of steam and water in said output header; meansassociated with said plenum and said water tube boiler means to minimizethe pressure drop of gas communicated through said enclosure; feed-watermeans in fluid communication with said input header to supply water tosaid boiler means; and separator means having a steam outlet pipe and influid communication with said output header to separate the steam andwater mixture output of said boiler means; steam pressure sensitivemeans in fluid communication with said steam outlet pipe to regulatesaid damper means to cause gas communication to said enclosure to varyinversely with the outlet steam pressure; and water level sensitivemeans in fluid communication with said feedwater means to regulate saiddamper means and prevent gas communication to said enclosure in theevent of failure of said feedwater means.

3. A closed system for the recovery of waste heat energy from hotexhaust gas from a heat source, said system having a boiler providedwith a source of feedwater in fluid communication with a steam-waterseparator and reservoir, comprising in combination: an insulatedenclosure in fluid communication with said source and having a dividedgas outlet to form an exhaust to atmosphere and a boiler gas inlet, saiddivided gas outlet provided with damper means to regulate the amount offlow of hot gas therethrough responsive to steam pressure at the outletof said separator, the water level in said separator and reservoir, andto feedwater pressure in the system; said boiler having internalcirculating water and mounted adjacent to said insulated enclosure inthe path of hot gas discharged from said boiler gas inlet, the boilerdesigned to transfer the heat energy of said hot exhaust gas dischargedfrom said boiler gas inlet to said circulating water to produce amixture of steam and water; water regulating means in fluidcommunication with said boiler to produce a predetermined excess of saidinternal circulating water; said separator adapted to separate saidmixture of steam and water and direct the water separated from themixture to said reservoir; liquid level sensing means in liquidcommunication with said separator and reservoir to sense the level ofwater in the separator and reservoir and control said damper means andsaid water regulating means to increase the volume of hot gas flowthrough said boiler gas inlet as said level of water increases and tocontrol said water regulating means to control the volume of flow ofsaid feedwater, and to prevent further the hot exhaust gas from beingconveyed through the boiler gas inlet when the liquid level reaches apredetermined low point; and means in fluid communication with the steamoutput of said separator to sense the pressure of the output steam andcontrol said damper means to increase the volume of hot gas flow throughsaid boiler gas inlet as said steam pressure decreases below a firstpredetermined level, decrease the volume of hot gas flow through theboiler gas inlet as the steam pressure increases above a secondpredetermined level, and prevent gas flow through the boiler gas inletwhen the steam pressure reaches a third predetermined level.

4. In a system for recovering heat energy from exhaust gases expelled bya source having an operating efficiency inversely proportional to theback pressure imposed thereon, the combination comprising: a boiler;means adjacent to said boiler and in fluid communication with saidsource to convey said exhaust gases away from the source and divideselectively the flow of the gases for exhaust to the atmosphere and tosaid boiler for heating, said means and said boiler arranged andconstructed to impose minimal obstruction to said exhaust gas flow forheating the boiler and cause relatively minor back pressure on saidsource; feedwater means in fluid communication with said boiler toprovide water for conversion to a mixture of water and steam; andautomatic regulating means associated with said means adjacent to saidboiler and said feedwater means responsive to the pressure of generatedsteam from the boiler, water pressure in the feedwater means, and thelevel of said water provided by the feedwater means, said regulatingmeans to control the selective division of the flow of gas in said meansadjacent to the boiler and the flow of Water provided by the feedwatermeans to cause a relatively constant predetermined level of steampressure at the outlet of said boiler in equilibrium with a selecteddivision of the flow of gas in said means adjacent to the boiler and theflow of Water provided by the feedwater means.

5. A boiler to produce a mixture of steam and water adapted for use inthe path of hot gases and provided with a source of feedwater,comprising: an inlet header pipe having one end capped and the other endin fluid communication with said source of feedwater; an outlet headerpipe having one end capped and the other end for discharging saidmixture of steam and Water, said outlet pipe in spaced parallel relationWith said inlet header; and a plurality of spaced apart spirally coiledtubes each having one end connected in fluid communication With saidinlet header and the other end connected in fluid communication withsaid outlet header, each said tube defining at least about four spiralturns grouped in pairs, adjacent turns of each said pair spacedrelatively close together and adjacent turns of successive pairs spacedapart a distance at least equal to the diameter of a said tube.

References Cited UNITED STATES PATENTS 1,053,491 2/1913 Grimm 122250 X1,332,943 3/1920 Cabena l22-480 2,060,290 11/1936 Ebner 122-7 2,578,05912/1951 Graham 165163 2,697,421 12/1954 Nalven 122-7 FOREIGN PATENTS94,992 12/ 1962 Denmark. 750,124 6/1956 Great Britain. 878,189 9/1961Great Britain.

CHARLES J. MYHRE, Primary Examiner.

